The present invention relates to a magnetic storage element and a magnetic storage device. More particularly, it relates to a magnetic storage element having a tunneling magnetoresistive effect, and a magnetic storage device using the same.
The magnetoresistive (MR) effect is a phenomenon that a magnetic substance is changed in electrical resistance by being applied with a magnetic field, and is used for a magnetic field sensor, a magnetic head, and the like. In recent years, as giant magnetoresistance: GMR effect materials exhibiting a very large magnetoresistive effect, artificial lattice films of Fe/Cr, Co/Cu, and the like have been introduced in the following Non-Patent Documents 1 and 2.
Whereas, there is proposed a magnetoresistive effect element using a multilayer structure having a non-magnetic metal layer with such a thickness as to eliminate the exchange coupling effect between ferromagnetic layers, and formed of ferromagnetic layer/non-magnetic layer/ferromagnetic layer/anti-ferromagnetic layer. In this element, the ferromagnetic layer and the anti-ferromagnetic layer are exchange coupled. Accordingly, the magnetic moment of the ferromagnetic layer is fixed, and only the spin of the other ferromagnetic layer can be reversed by an external magnetic field with ease. This is an element known as a so-called spin-valve structure. In this element, the exchange coupling between the two ferromagnetic layers is weak, and hence the spin can be reversed by a small magnetic field. For this reason, the spin valve structure can provide a magnetic storage element having a higher sensitivity with respect to the magnetic field as compared with the exchange coupled film. As the anti-ferromagnetic substance, there is used FeMn, IrMn, PtMn, or the like. The spin valve structure passes a current in the film in-plane direction when used. However, due to the foregoing feature, it is used for a high-density magnetic recording reproduction head.
On the other hand, use of the perpendicular magnetoresistive effect of passing a current in the direction perpendicular to the film plane provides a further larger magnetoresistive effect. This is disclosed in, for example, the following Non-Patent Document 3.
Further, the TMR: tunneling magnetoresistive effect due to the ferromagnetic tunneling junction is also disclosed in, for example, the following Non-Patent Document 4. The tunneling magnetoresistance is obtained by using the following fact: in a three-layer film formed of ferromagnetic layer/insulation layer/ferromagnetic layer, the directions of spins of the two ferromagnetic layers are changed into the same direction as each other or the opposite directions to each other; thus, the magnitude of the tunneling current in the direction perpendicular to the film plane varies depending on the directions of the spins.
In recent years, studies for using GMR and TMR elements for a nonvolatile magnetic storage semiconductor device (MRAM: magnetic random access memory) have been disclosed in, for example, the following Non-Patent Documents 5 to 7.
In this case, there is studied a pseudo-spin valve element or a ferromagnetic tunneling effect element in which a non-magnetic metal layer is sandwiched between two ferromagnetic layers having different coercive forces. When used for a MRAM, the elements are arranged in a matrix. A current is passed through a separately disposed wire to apply a magnetic field thereto. Thus, the two magnetic layers forming each element are controlled. Herein, by controlling the two magnetic layers in the same direction, “1” is recorded. Whereas, controlling the two magnetic layers in opposite directions to each other, “0” is recorded. Reading is performed using the GMR effect or the TMR effect.
For a MRAM, use of the TMR effect results in a lower power consumption than the use of the GMR effect. For this reason, use of TMR elements has been mainly studied. The MRAM using the TMR elements has the following features: a larger output voltage can be obtained because the resistance change ratio at room temperature is as large as 20% or more and the resistance at the tunneling junction is large; and a current for reading is much smaller because spin reversal is not required to be performed for reading; and other features. For these reasons, the MRAM using the TMR elements is expected as a low power consumption type nonvolatile semiconductor storage device capable of high-speed writing/reading.
In the write operation of the MRAM, it is desired to control the magnetic characteristics of the ferromagnetic layers in the TMR element. Specifically, there are demands for a technology of controlling the relative magnetization directions of the two ferromagnetic layers interposing a non-magnetic layer to the same direction, or the opposite directions, and a technology of causing magnetization reversal in one magnetic layer in a desirable magnetic storage element with reliability and efficiency. The technologies of uniformly controlling the relative magnetization directions of the two ferromagnetic layers interposing a non-magnetic layer to the same direction or opposite directions in the film plane by using two crossing wires are shown in, for example, the following Patent Documents 1, 3, 4, and 7.
Further, in a MRAM, when miniaturization of magnetic storage elements is performed for high integration, the reversed magnetic field increases due to the demagnetization field depending upon the size in the film plane direction of the magnetic layer. As a result, a large magnetic field becomes necessary for writing, and the power consumption also increases. For this reason, as indicated in, for example, the following Patent Documents 2, 5, 6, and 7, there are proposed the technologies of optimizing the shape of the ferromagnetic layer, and facilitating the magnetization reversal.
When miniaturization of magnetic storage elements is performed with an increase in integration density in a MRAM, a further larger magnetic field becomes necessary for writing due to the effect of the demagnetization field. This results in a larger effect of the magnetic field exerted on the periphery of the selected magnetic storage element. Accordingly, erroneous magnetization reversal becomes remarkable. In order to cope with this, a wire covered with a material having a high magnetic permeability such as Permalloy is formed, so that a magnetic field is concentrated to a TMR element. This is proposed in, for example, the following Patent Document 3.